The present invention relates to a clock skew measurement apparatus and a clock skew measurement method by which a skew between a plurality of clock signals distributed by a clock distribution circuit is measured.
A clock skew has conventionally been estimated statistically using a time interval analyzer or a frequency counter. That is, as shown in FIG. 1, for example, when a reference clock signal CLKg from a clock signal source 11 is distributed and supplied to registers 12j and 12k, each of the clocks under measurement CLKj and CLKk in the respective registers 12j and 12k is inputted to a time interval analyzer 13, where a timing difference between a zero-crossing point of the clock signal under measurement CLKj and a zero-crossing point of the clock signal under measurement CLKk is measured, and a fluctuation of the timing difference is measured by a histogram analysis. An example of clock skew measurement using a time interval analyzer 13 is described in, for example, “Jitter Analysis Clock Solutions”, Wavecrest Corp., 1998.
However, there is a problem in this clock skew measurement method using the time interval analyzer that it takes a long time to acquire a number of data required for the histogram analysis since, it requires an intermediate dead-time until clock skew measurement can be repeated. In addition, in the clock skew measurement method using the time interval analyzer, a skew between clocks having different frequencies cannot be measured. Therefore, a new clock skew measurement method is required for a precise control of a local clock and a global clock.
It is an object of the present invention to provide a measurement apparatus of a skew between clocks and its method by which a skew between clocks can be measured in a short time compared with a conventional apparatus and its method.
It is another object of the present invention to provide a measurement apparatus of a skew between clocks and its method by which a skew between clocks having different frequencies can be estimated.